The present invention relates to fluid control valves etched from monocrystalline substrates such as silicon.
It is known to etch nozzles, such as ink jet nozzles, from silicon substrates utilizing batch processing techniques found in the semiconductor industry. Precision components comparable to precision machined metal components have been achieved without the complexity and labor intensity of metal machining processes. More compact and reliable nozzles have resulted.
Attempts have also been made to replace machined control valves with semiconductor devices. For example, U.S. Pat. No. 4,585,209 to Aine et al discloses a gas valve for controlling the flow of gaseous material. A silicon cantilevered leaf spring is disposed overlying an apertured plate. The cantilever is electrically isolated from the valve plate by a coating of thin insulating material applied over the valve plate. Gas pressure applied against the cantilever opens the valve by bending the cantilever. An electrostatic potential applied between the cantilever and plate bends the cantilever back over the plate to reduce or shut off the gaseous flow. A disadvantage of this approach is that the pressure force applied by the gas must be overcome by the combination of cantilever spring force and electrostatic attraction in order to seal the valve. Thus, this apparatus does not appear to be suitable for controlling fluids under higher pressures such as, for example, the fluid pressures in which automobile fuel injectors must operate. Still another disadvantage, is the potential for electrical arcing between the valve plate and cantilever which would be unacceptable in applications utilizing flammable fluids. Another disadvantage is that at low fluid pressures, there may be insufficient gas pressure to overcome the stiffness of the cantilever thereby preventing actuation of the valve.
An approach using silicon valves wherein pressurized fuels are controlled is disclosed in U.S. Pat. Nos. 4,628,576 and 4,647,013, both issued to Giachino et al. However, this approach requires mechanical springs, or equivalent structures, for seating the valve. More specifically, an etched substrate having a diaphragm and downward facing mesa is shown positioned over a substrate having a nozzle in alignment with the mesa. The substrates are etched such that fluid enters from the sides and exits through the outlet nozzle. A piezoelectric wafer is bonded to the top of the diaphragm. Attached to the top of the wafer is a coil return spring. A smaller spring disposed under the outlet nozzle pushes the lower substrate against the mesa for sealing the valve during the off state. In operation, the piezoelectric wafer pushes against the coil spring to lift the mesa away from the outlet orifice in response to the application of electrical power. When electrical power is removed, the wafer relaxes, enabling the return spring to downwardly deflect the mesa against the outlet orifice. A disadvantage of this approach is its size and complexity, requiring two mechanical springs and a piezoelectric wafer of sufficient size to overcome the force of the mechanical return spring.